A liquid crystal display is spreading in its applications in recent years, as an image display apparatus of a low electric power consumption capable of space saving. A large viewing angle dependence of the displayed image has been considered a major drawback of the liquid crystal display, but a VA liquid crystal mode of a wide viewing angle, recently commercialized, is rapidly increasing the application of the liquid crystal display even in a market requiring a high-quality image such as a television.
Along with such trend of the liquid crystal display, further improvements are being required in the optical compensation ability of an optical compensation member, employed for improving color and contrast, and a viewing angle dependence thereof.
In the optical compensation film for a liquid crystal display of VA mode, JP-A-2004-326089 discloses a technology of constructing a negative C-plate and a positive A-plate, employed for improving the viewing angle characteristics of the liquid crystal display, in a layered structure with a specified combination of wavelength dispersion characteristics, thereby realizing a liquid crystal display of satisfactory color reproducibility, with a high contrast and without an unevenness caused by interference or a color shift. However, in this technology, in case base films of the A-plate and the C-plate are used as protective films of the polarizer, such films are difficult to adhere to a polarizing film and have to be made tacky, thereby resulting in an elevated cost.
Also JP-A-2004-325523 describes a technology of providing a retardation film showing excellent phase difference characteristics over a wide range (from a short wavelength region to a long wavelength region) and showing a satisfactory antireflective property in a short wavelength region and a long wavelength region when employed in a reflective LCD, by a single retardation film which is formed by mixing a resin having a positive refractive index anisotropy, a resin having a negative refractive index anisotropy and a retardation regulating agent showing a dichroic property, or which is formed by mixing a copolymer resin having a repeating unit constituting a polymer with a positive refractive index anisotropy and a repeating unit constituting a polymer with a negative refractive index anisotropy, and a retardation regulating agent mentioned above. This technology is however associated with drawbacks that the materials for preparing the film are inevitably expensive and that the film involves a high production cost and a poor mass producibility.
Also JP-A-2004-325971 discloses a technology of utilizing a laminated phase difference plate showing a birefringence, formed by stretching a layered product containing at least one each of a first layer, principally constituted of a material showing a positive intrinsic birefringence, and a second layer, principally constituted of a material showing a negative intrinsic birefringence, thereby realizing a liquid crystal display of satisfactory color reproducibility, with a high contrast and without an unevenness caused by interference or a color shift. However in this method, the layered product having different softening temperatures is stretched at a certain temperature which is inevitably different from an optimum stretching temperature of each layer, thereby being unable to exhibit a sufficient performance.
Also WO2004/068226 A1 discloses a technology of executing an optical compensation with a polymer film having different wavelength dispersions in a retardation in planar direction and a retardation in thickness direction, thereby further improving a contrast and obtaining a color in a black-display state closer to gray by means of a single compensation film. However this technology is insufficient in optimizing the retardation. Also JP-A-2004-326089 discloses a technology, for realizing the above-mentioned wavelength dispersion characteristics, of utilizing a laminated retardation film formed by laminating, on a stretched polymer film having an inverse wavelength dispersion characteristics in which the retardation becomes smaller at a shorter wavelength, a coated layer having a normal wavelength dispersion characteristics in which the retardation becomes larger at a shorter wavelength. This method, however, involves a complex manufacturing process because of the laminated structure, thus being insufficient in the productivity and the cost.